Thursday, July 5, 2012

When Protons Collide: New Particle Observed at Large Hadron Collider

Search
for Higgs boson reveals new particle

Physicists on experiments at the Large
Hadron Collider have oberved a new particle that future analysis may show to be
the long-sought Higgs boson, the missing piece in the Standard Model of
particle physics.

Last December, the CMS and ATLAS
experiments announced seeing tantalizing hints of a new particle in their hunt
for the Higgs. Since then, they have more than doubled their collected data,
which has led to today's announcement. Involved in this international effort
were more than 1,700 scientists, engineers, technicians and graduate students from
U.S. institutions, who helped design, build and operate the LHC accelerator and
its four particle detectors.

Scientists on experiments at the LHC
announced their latest results at a seminar at the home of the LHC, the CERN
laboratory, on the border of Switzerland and France. Physicists from across the
United States gathered at laboratories and universities in the middle of the
night to watch a live-stream of the seminar online. Scientists will give more
detailed presentations about the results this week at the biannual
International Conference on High Energy Physics, held this year in Melbourne,
Australia.

"What has been announced today
could not have been accomplished without the cooperation of scientists and
nations throughout the world in seeking an understanding of the fundamental
laws of nature," said Ed Seidel, NSF's assistant director for the Mathematical
and Physical Sciences. "If the particle announced today at CERN is
confirmed to be the Higgs boson, this represents a keystone in our knowledge of
the elementary forces and particles that exist in our universe."

Through more than four decades of experimental
tests, researchers have found that the Standard Model of particle physics has
correctly predicted and explained the elementary particles and forces of
nature. But the Standard Model cannot, without the Higgs boson, explain how
most of these particles acquire their mass, a key ingredient in the formation
of our universe.

In 1964 scientists proposed the
existence of a new particle, now known as the Higgs boson, whose coupling with
other particles would determine their mass. Many experiments have searched for
the Higgs boson, but it has eluded detection. Only now, after decades of
developments in accelerator and detector technology and computing--not to
mention advancements in the understanding of the rest of the Standard
Model--are scientists approaching the moment of knowing whether the Higgs was
the right solution to this problem.

"Up until now, we've been guided by
theory," said University of California Santa Barbara physicist Joe
Incandela, spokesperson of the CMS experiment. "If we start to see something
in our experiment, we have a new guide. It's nature. It's the real thing."

When protons collide in the Large Hadron
Collider, their energy can convert into mass, often creating short-lived
particles. These particles quickly decay into lighter, more stable particles
that scientists can record with their detectors.

Theoretical physicists have predicted
the rate at which the Higgs boson will be produced in high energy proton-proton
collisions at the LHC, and also how it decays into certain combinations of
observable particles. Experimental physicists at ATLAS and CMS have been
studying the collisions and have seen evidence of a new particle that decays in
a manner consistent with the predictions for the Higgs. They will need to
collect more data and run further analysis to determine the properties of the
new particle.

"If the Higgs boson is discovered,
attention will turn to a new set of important questions," said University
of California Irvine physicist Andy Lankford, deputy spokesperson of ATLAS.
"Is this new particle a Standard Model Higgs, or is it a variant that
indicates new physics and other new particles?"

Discovery of the Higgs--or another new
particle--would represent only the first step into a new realm of understanding
of the world around us.